DESCRIPTION: This is a proposal to find new components of a plant pathogen-response signal transduction pathway. As such, it is in the general area of eukaryotic signal transduction, and among eukaryotic signal transduction pathways the gene-for-gene plant resistance pathway is unique and just beginning to be understood. The background is that plant pathogens, in this case the bacterium Pseudomonas syringae carrying the avrRpt2 avirulence gene, induce a plant response that depends on the specific avirulence gene and on a plant resistance gene. The Arabidopsis resistance gene that responds to avrRpt2 is RPS2; when active it causes plants to have a hypersensitive response that limits pathogen growth. Recent cloning of RPS2 by two groups (one including the PI) shows it to code a protein with a leucine zipper near the amino terminus, a nucleotide triphosphate binding loop and near the carboxy- terminal end a series of leucine rich repeats, of the type found in receptors, and in other proteins that are activated by protein- protein contacts, such as yeast adenylate cyclase.